Changeover valve and flow control valve assembly having the same

Abstract: A flow control valve assembly which shows high liquid-tightness and good flow controllability even if a high-pressure, low-viscosity fluid is used. It has a housing (1) formed with an inlet port (2) and an outlet port (3), and a spool (4) inserted in the housing. First and second fluid chambers (5,6) for applying fluid pressures on both ends of the spool communicate with each other through a fluid passage (8) having an orifice (7). The opening of the valve portion is adjusted by the movement of the spool so that the spool driving force produced by the difference in the pressures applied to both ends of the spool balances with the force of a biasing means (10), whereby a fluid flows through the orifice at a controlled rate. This control valve assembly has an elastic annular seal (11). When the spool moves toward the annular seal, the land portion on the spool outer periphery is adapted to butt the seal, thereby closing the fluid passage. In this closed state, fluid leakage is reduced substantially to zero. Also, it is possible to control the fluid flow even while the flow rate is very low.

Description: This invention relates to a changeover valve adapted for use in a hydraulic system, such as an automotive brake system, which is required to delicately control the flow of high-pressure, low-viscosity hydraulic fluid within a wide range of flow rate, and a flow control valve assembly including the changeover valve. Fig. 4 shows a conventional flow control valve assembly having a housing 1 formed with an inlet port 2 and an outlet port 3, and a spool 4 substantially liquid-tightly and slidably mounted in the housing 1. A first fluid chamber 5 and a second fluid chamber 6 which exert fluid pressure on both ends of the spool 4 communicate with each other through a fluid passage 8 having an orifice 7. A valve portion 9 is formed by a land portion formed on the inner surface of the housing 1 and a land portion formed on the outer surface of the spool which are brought into opposed position to each other. The fluid passage in the valve is opened and closed by the valve portion 9. The spool is biased by a biasing means 10. Thus, the controlled flow rate in the valve depends upon the biasing force of the biasing means 10. In this control valve assembly, the spool 4 is biased by the biasing means 10 in a direction opposite to the direction of force applied to the spool by the pressure difference between the first and second fluid chambers 5 and 6. The spool 4 tends to move toward a point at which the pressures on both ends thereof balance with each other. Thus, the degree of opening of the valve portion 9 is automatically adjusted so that the above-mentioned pressure difference balances with the force of the biasing means 10. As a result, hydraulic fluid flows through the second fluid chamber 6 to the outlet port 3 at a rate determined by the pressure difference and the sectional area of the orifice 7. If more accurate fluid flow control is desired, as shown in Fig. 5, the valve portion 9 may be formed by an elastic annular seal 11 provided around the outer periphery of the spool and a shoulder formed on the outer periphery of the spool and adapted to be brought into contact with the seal 11. This arrangement is disclosed in Unexamined Japanese Patent Publication 3-223578 and EP-A-0 434 092 filed by the applicant of the present invention. One problem with the flow control valve assembly of Fig. 4 is that a certain degree of fluid leakage is inevitable because some degree of gap is inevitably formed between the land portion on the housing inner surface and the land portion on the spool outer surface. Such leakage results in error in flow rate. Thus, this type of valve is not suitable for use in a hydraulic system used to control the flow rate of a low-viscosity, high-pressure hydraulic fluid with high accuracy. The flow control valve assembly shown in Fig. 5 is free of fluid leakage because the spool shoulder is brought into tight contact with the elastic annular seal 11. But if a clearance 12 between the outer periphery of the spool 4 and the inner periphery of the housing 1, which is a part of the hydraulic fluid passage, is too wide, the seal 11 may get caught in the clearance and damaged. Thus, the clearance 12 has to be narrow. But, with a narrow clearance 12, the valve cannot pass a large flow rate. Such a control valve assembly has limited use. US-A-2,633,147 discloses a safety shutoff valve for air brake systems including a control cylinder carrying a neoprene washer. This valve is used to shut off the flow of air guided to brake diaphragms in case the pressure exceeds a predetermined value, i.e. under abnormal conditions. However, this valve is not suitable for use as a control device in order to delicately control the flow of a high-pressure, low-viscosity hydraulic fluid in a hydraulic system. An object of the present invention is to provide a flow control valve assembly which solves the problems. According to the present invention, there is provided a changeover valve including a housing having an inlet port and an outlet port and formed with a land portion on the inner peripheral surface thereof, and a spool slidably and substantially liquid-tightly mounted in the housing and formed with a land portion on the outer peripheral surface thereof, the land portions formed on the housing inner periphery and the spool outer periphery being adapted to be brought into opposed position to each other to close and open a fluid passage extending from the inlet port to the outlet port, characterized in that: the housing has in inner surface thereof an annular groove in which is liquid-tightly mounted an annular seal made of an elastic material, the land formed on the spool outer periphery being adapted to come into contact along edge thereof with the annular seal, thereby closing the fluid passage, when the spool moves toward the annular seal until the land portion on the spool outer periphery abuts the annular seal. The flow control valve assembly according to the present invention is disclosed in independent claims 2 and 4. If the elastic annular seal is adapted to be brought into contact with the edge of the land formed on the outer periphery of the spool, it is liquid-tightly inserted in an annular groove formed in the inner periphery of the housing. If it is adapted to be brought into contact with the edge of the land formed on the housing inner periphery, it is liquid-tightly inserted in an annular groove formed in the outer periphery of the spool. An inevitable gap is formed in the valve portion comprising the land portion on the housing inner periphery and the land portion on the spool outer periphery which are adapted to be brought into slidal contact with each other. But since the edge of the land portion formed on the spool or the housing is brought into tight contact with the annular seal, it is possible to close the fluid passage by the annular seal and thus to completely close the valve without any fluid leakage. A fluid passage having a sufficient sectional area is formed inside the seal if the annular seal is inserted in the annular groove formed in the inner periphery of the housing, and around the seal if the annular seal is inserted in the annular groove formed in the outer periphery of the spool. In either case, no clearance similar to the clearance 12 shown in Fig. 5 is formed. This arrangement permits a large fluid flow to pass while preventing the seal from getting caught in such a clearance. While the spool biasing force is extremely small, the flow rate is controlled in a very narrow range according to the varying degree of opening between the seal and the spool. While the biasing force is moderately small, the flow rate is controlled with the varying length of slidal contact between the land portion on the spool outer periphery and the land portion on the housing inner periphery (or gap width in the valve portion). When the biasing force is rather large, the flow rate is controlled as the degree of opening of the main fluid passage varies. Thus, the flow rate can be controlled within a wide range. Thus, according to the present invention, while the valve is closed, it maintains good liquid-tightness. While the flow rate is low, it can be controlled reliably. When the travel distance of the spool increases, the fluid chamber in which one end of the spool is disposed will come into direct communication with the port. Thus, it is possible to sufficiently increase the fluid flow rate. Further, since the gap at the valve portion is extremely narrow, the annular seal will never be damaged. Such a flow control valve assembly is of high performance and reliable. Other features and objects of the present invention will become apparent from the following description made with reference to the accompanying drawings, in which: Fig. 1 is a sectional view of an embodiment of the flow control valve assembly according to the present invention; Fig. 2(a) is an enlarged view of the portion enclosed in chain line of Fig. 1 showing the state in which the biasing force is zero; Fig. 2(b) is a similar view showing the state in which it is small; Fig. 2(c) is a similar view showing the state in which it is large; Fig. 3 is a sectional view of another embodiment; Fig. 4 is a view showing a conventional flow control valve assembly; and Fig. 5 is a view showing another conventional flow control valve assembly. Fig. 1 shows an embodiment of the flow control valve assembly including the changeover valve according to the present invention. The flow control valve assembly has a housing 1 formed with an inlet port 2 and an outlet port 3, and a spool 4. Numeral 5 and 6 designate a first fluid chamber leading to the inlet port and a second fluid chamber for discharging fluid toward the outlet port 3, respectively. The first and second fluid chambers communicate with each other through a fluid passage 8 having an orifice 7. In the embodiment, the fluid passage 8 is formed in the spool 4, but such a passage having an orifice may be formed in the housing 1. A valve portion 9 is formed by a land portion formed on the inner surface of the housing 1 and a land portion formed on the outer surface of the spool 4 which are brought into opposed position to each other. The fluid passage in the valve is opened and closed by the valve portion 9. Fluid from the second fluid chamber 6 flows through the valve portion 9 to the outlet port 3. The spool 4 is biased downwards in the figure by a biasing means 10. In the embodiment, the biasing means is an electromagnet whose biasing force is variable by electronically controlling the current applied thereto. An annular seal 11 of an elastic material is provided in the second fluid chamber 6. The spool 4 is adapted to come into contact along its edge with the seal 11. While the biasing force F of the biasing means 10 is zero, the spool 4 is pushed to the extreme end of its movement toward the second fluid chamber 6 and kept in contact with the annular seal 11. In this state, the fluid flow between the inlet port 2 and the outlet port 3 is substantially zero except slight leakage through a gap formed around the outer periphery of the spool. When the electromagnet is energized, the spool 4 is moved by its biasing force F, so that the degree of opening of the fluid passage extending from the second fluid chamber 6 to the outlet port 3 will be adjusted automatically. While the biasing force F is extremely small, such an adjustment of the opening is made between the annular seal 11 and the spool 4. While the force F is moderately small, the opening is adjusted with variation in the length L1 (Fig. 2(b)) of contact between the land portion on the spool outer periphery and the land portion on the housing inner periphery. When the force F is rather large, such an adjustment is made by the amount of opening L2 (Fig. 2(c)) of the outlet port 3. The degree of opening of the fluid passage is thus automatically adjusted to such a value that the fluid pressure difference between the first and second fluid pressure chambers 5 and 6 balances with the biasing force F. Therefore, the controlled fluid flow rate, which is determined by the pressure difference and the sectional area of the orifice 7, is proportional to the biasing force F. The length A (in Fig. 2(a)) of contact at the valve portion 9 can be made substantially shorter than the corresponding contact length in the control valve of Fig. 4. This is because, in the arrangement of Fig. 4, rather long contact length A is needed to prevent fluid leakage, whereas in the arrangement of the present invention, the annular seal 11 serves to prevent fluid leakage and thus the length A need not be so long. Because the contact length at the valve portion may be minimum, there is no possibility of the seal 11 getting caught in the valve portion. If the valve is a constant-flow control valve, the orifice 7 may have a constant sectional area as shown in Fig. 1. Also, the biasing means 10 may be of a type whose biasing force is constant, such as a spring. Fig. 3 shows another embodiment of the present invention. The valve assembly of this embodiment has a housing 101 formed with an inlet port 102 and an outlet port 103, a spool 104, a first fluid chamber 105, and a second fluid chamber 106 leading to an outlet port 103. The first and second fluid chambers 105, 106 communicate with each other through a fluid passage 108 having an orifice 107. The orifice 107 is defined by the housing 101 and a valve body 112 and its sectional area is variable. Its sectional area changes as the valve body 112 moves to a position where the electromagnetic force produced by a current that flows through a coil 113 balances with the force of a spring 114. Numeral 109 indicates a valve portion comprising a land portion on the housing inner periphery and a land portion on the spool outer periphery which are brought into slidal contact with each other. The fluid passage between the inlet port 102 and the first fluid chamber 105 is opened and closed by the valve portion 109. The spool 104 is biased upwards by a biasing means 110, which is, in this embodiment, a spring having a constant force. An elastic annular seal 111 is fixed to the spool 104 in a third fluid chamber 115 having a diameter larger than the diameter of the seal and is adapted to be brought into contact with the edge of the land portion on the inner periphery of the housing 101. In this embodiment, the annular seal 111 is fixed to the spool 104 and the spring 110 has a constant biasing force. The flow rate is controlled through the variable orifice. But since its function and effects are the same as with the first embodiment, their detailed description is omitted. The mounting position of the annular seal, whether or not the biasing force is variable, and whether or not the sectional area of the orifice is variable may be determined freely taking into consideration the property of the fluid used and the required range of flow rate. If both the biasing force and the orifice sectional area are variable, one of them may be changeable between two steps while the other is variable in a plurality of steps or steplessly. The changeover valve according to the present invention is applicable not only to a flow control valve assembly but also to a flow direction changeover valve or a pressure control valve. It is particularly suitable where both high fluid-tightness (while closed) and high flow rate (while opened) are required. The flow control valve assembly according to the present invention is also not limited to the specific types of the embodiments but may be of the type proposed by the applicant of the present invention in Unexamined Japanese Patent Publication 3-234987.

Claims: A changeover valve including a housing (1) having an inlet port (2) and an outlet port (3) and formed with a land portion on the inner peripheral surface thereof, and a spool (4) slidably and substantially liquid-tightly mounted in said housing (1) and formed with a land portion on the outer peripheral surface thereof, said land portions formed on the housing inner periphery and the spool outer periphery being adapted to be brought into opposed position to each other to close and open a fluid passage (8) extending from said inlet port (2) to said outlet port (3), characterized in that said housing (1) has, in an inner surface thereof, an annular groove in which is liquid-tightly mounted an annular seal (11) made of an elastic material, said land portion formed on the spool outer periphery being adapted to come into contact with said annular seal (11), thereby closing said fluid passage (8), when said spool (4) moves toward said annular seal (11) until said land portion on the spool outer periphery abuts said annular seal (11). A flow control valve assembly including a changeover valve comprising a housing (1) having an inlet port (2) and an outlet port (3) and formed with a land portion on an inner peripheral surface thereof, a spool (4) slidably and substantially liquid-tightly mounted in said housing (1) and formed with a land portion on an outer peripheral surface thereof, and a first fluid chamber (5) and a second fluid chamber (6) provided at both ends of said spool (4) to exert fluid pressure on said spool (4) and communicating with each other through a fluid passage (8) having an orifice (7), said land portions formed on the housing inner periphery and the spool outer periphery being adapted to be brought into opposed position to each other to form a valve portion (9) to close and open said fluid passage (8) extending from said inlet port (2) to said outlet port (3), and a biasing means (10) for biasing said spool, characterized in that said housing (1) has, in an inner surface thereof, an annular groove in which is liquid-tightly mounted an annular seal (11) made of an elastic material, said land portion formed on the spool outer periphery being adapted to come into contact with said annular seal (11), thereby closing said fluid passage (8), when said spool (4) moves toward said annular seal (11) until said land portion on the spool outer periphery abuts said annular seal (11), wherein the degree of opening at said valve portion (9) of said changeover valve is automatically adjusted by the movement of said spool (4) so that the spool driving force produced by the fluid pressure difference between said first (5) and second (6) fluid chambers balances with the biasing force of said biasing means (10) that counteracts said spool driving force, whereby a fluid flows through said orifice (7) to said outlet port (3) at a rate determined by said fluid pressure difference and the sectional area of said orifice (7). A fluid flow control valve assembly as claimed in claim 2, wherein said biasing means (10) is an electromagnet whose biasing force is variable and electronically controlled. A flow control valve assembly including a changeover valve comprising a housing (101) having an inlet port (102) and an outlet port (103) and formed with a land portion on an inner peripheral surface thereof, a spool (104) slidably and substantially liquid-tightly mounted in said housing (101) and formed with a land portion on an outer peripheral surface thereof, and a first fluid chamber (105) and a second fluid chamber (106) provided at both ends of said spool (104) to exert fluid pressure on said spool (104) and communicating with each other through a fluid passage (108) having an orifice (107), said land portions formed on the housing inner periphery and the spool outer periphery being adapted to be brought into opposed position to each other to form a valve portion (109) to close and open said fluid passage (108) extending from said inlet port (102) to said outlet port (103), and biasing means (110) for biasing said spool (104), characterized in that said spool (104) has, in an outer peripheral surface, an annular groove in which is liquid-tightly mounted an annular seal (111) made of an elastic material, said annular seal (111) being adapted to come into contact with said land portion formed on the housing inner periphery, thereby closing said fluid passage (108), when said annular seal (111) mounted on said spool (104) moves towards said land portion on the housing inner periphery until said annular seal (111) abuts said land portion on the housing inner periphery, wherein the degree of opening at said valve portion (109) of said changeover valve is automatically adjusted by the movement of said spool (104) so that the spool driving force produced by the fluid pressure difference between said first (105) and second (106) fluid chambers balances with the biasing force of said biasing means (110) that counteracts said spool driving force, whereby a fluid flows through said orifice (107) to said outlet port (103) at a rate determined by said fluid pressure difference and the sectional area of said orifice (107), and in that said biasing means (110) is an electromagnet whose biasing force is variable and electronically controlled. A fluid flow control valve assembly as claimed in one of claims 2 to 4, characterized in that it further comprises a valve body (112), wherein said orifice (107) has a variable sectional area by moving said valve body (112) under the force of a spring (114) and the force of an electronically controlled electromagnet (113) which are applied to said valve body (112) from opposite directions. A fluid flow control valve assembly as claimed in claim 5, as far as this claim is dependent on claim 3 or 4, characterized in that the biasing force exerted on said spool (4; 104) and the sectional area of said orifice (107) are both variable.

Inventors: HASHIDA KOICHI, HASHIDA, KOICHI, HASHIDA, KOICHI, C/O ITAMI WORKS OF SUMITOMO EL.
Applicants: SUMITOMO ELECTRIC INDUSTRIES, SUMITOMO ELECTRIC INDUSTRIES, LIMITED
Application year: 1994
Main classification: B60T13
IPC codes: B60T8, G05D16, B60T15, G05D7